This invention relates to drawing instruments and, more particularly, to drawing instruments used in conjunction with computers for teaching the basic elements of computer programming.
Drafting instruments have long been used with computers to turn out precise representations of the material produced by the computer. As the use of computers has burgeoned and spread to the home, means of teaching the use and programming of such computers has become imperative. One of the outgrowths of this has been the generation of more and more higher level languages which are more easily conceptualized by the beginning operator.
An especially useful one of these languages, referred to by the trademark LOGO, has been devised by the Massachusetts Institute of Technology. An especially desirable feature of this language is that it allows a person learning the language to realize results with each step of learning rather than having to wait until an entire program has been produced. One of the features of the LOGO language is that the cursor (called a Turtle in LOGO) which appears on the screen, moves with each simple command, leaving, if desired, a track behind indicating where it has been. This track may be used as the output by the operator. As will be recognized, this ability makes it quite simple for a beginner to visualize and to program graphics. For this reason, LOGO has become one of the most used languages for the teaching of computer basics.
In conjunction with the LOGO language, a piece of peripheral drawing equipment has been produced which physically emulates the cursor and produces a printed output of the track followed by the turtle cursor on the cathode ray tube. This product, which is marketed as the Terrapin Turtle by Terrapin Inc. of Cambridge, Mass., is connected to a personal computer by an umbilical cord of wires through which it receives messages generated by the computer. These messages cause the device to follow a path over an output medium such as paper and produce a copy of the path (although it may be to a substantially different scale) followed by the cursor on the screen. The device has been especially useful in teaching children to program using the LOGO language because it reacts like a toy robot to the child's commands and provides a permanent output thereby turning into a game what might otherwise be a tedious learning situation.
The peripheral turtle is mechanized by a platform mounted on wheels which move it over the drafting medium in response to the commands of the computer. The platform carries a pen which may be lowered upon command to touch the surface of the paper and leave a track as the device moves.
The wheels which move the device are a pair which are positioned equidistant from and on opposite sides of the pen so that a line drawn through the lowered pen point passes through the point at which each of the wheels touches the surface of the drawing paper. Each of these wheels is mounted on a fixed axis running in a line which is parallel to the line through the pen point and the points where the wheels touch the paper. Each is driven by a bidirectional motor. Thus, by rotating each wheel in the same direction at the same rate, the pen point may be made to describe a straight line on the drawing paper; by rotating the wheels at the same rate in opposite directions, to describe a point; and by rotating the wheels at different rates in the same or different directions, to selectively draw any shape of line. Obviously, lifting the point increases the complication of the drawing which may be described.
The mechanical turtle works very well in theory and when well tuned. However, it does have certain inherent problems. First, the motors used to direct the movement of the device must be and remain very accurate for a line to be described which is a precise replica of what is desired. For example, in drawing a straight line the two wheels must move at precisely the same speed or the line will vary in one direction or the other, and possibly in both.
Not only must the motors and the wheels they drive be and remain quite precise, but the computer instructions given to those motors to cause them to operate so that a particular line may be described are quite complicated. For example, to make a circle using this device, it is necessary to cause both wheels to operate at different speeds so that the point describes a curved line having a constant radius from a point. If the circle is smaller in radius than the distance from the pen point to one of the wheels, one form of algorithm is required to operate the wheels, while if the radius is larger than that distance, a different algorithm is required. And with each of these algorithms, the two wheels of the device must move a different rates. This causes the memory space required to provide instructions to accomplish the movement of the device to be quite significant with relations to other aspects of the memory.
The device of this invention accomplishes the same drawing in what outwardly appears to be the same manner while using a greatly simplified mechanical apparatus which allows greatly simplified computer instructions requiring significantly less memory. Furthermore, the device of this invention accomplishes the foregoing while being significantly less subject to variations in mechanical properties which can cause the prior art device to malfunction in producing its output drawings.
It is therefor, an object of the present invention to provide an improved drawing device for use with a computer.
It is another object of the present invention to improve the accuracy with which a peripheral device may be used to describe drawings of various sorts.
It is another object of the present invention to reduce the cost of peripheral drawing devices used with computers.
An additional object of the present invention is to reduce the mechanical complexity of drawing devices used with computers.
Another object of the present invention is to reduce the complexity of the programming needed for operating drawing devices used with computers.